public SyntaxToken Lex()
{
if (_position >= _text.Length)
{
return(new SyntaxToken(SyntaxKind.EndOfFileToken, _position, "\0", null));
}
if (IsDigit(Current))
{
int start = _position;
while (IsDigit(Current))
{
Next();
}
int length = _position - start;
string text = _text.Substring(start, length);
int.TryParse(text, out int value);
return(new SyntaxToken(SyntaxKind.NumberToken, start, text, value));
}
if (char.IsWhiteSpace(Current))
{
int start = _position;
while (char.IsWhiteSpace(Current))
{
Next();
}
int length = _position - start;
string text = _text.Substring(start, length);
int.TryParse(text, out int value);
return(new SyntaxToken(SyntaxKind.WhitespaceToken, start, text, value));
}
switch (Current)
{
case '+':
Next();
SyntaxKind plusToken = SyntaxKind.PlusToken;
return(new SyntaxToken(plusToken, _position, plusToken.ToText(), plusToken.ToText()));
case '-':
Next();
SyntaxKind minusToken = SyntaxKind.MinusToken;
return(new SyntaxToken(minusToken, _position, minusToken.ToText(), minusToken.ToText()));
case '*':
Next();
SyntaxKind starToken = SyntaxKind.StarToken;
return(new SyntaxToken(starToken, _position, starToken.ToText(), starToken.ToText()));
case '/':
Next();
SyntaxKind slashToken = SyntaxKind.SlashToken;
return(new SyntaxToken(slashToken, _position, slashToken.ToText(), null));
case '(':
Next();
SyntaxKind openParenthesisToken = SyntaxKind.SlashToken;
return(new SyntaxToken(openParenthesisToken, _position, openParenthesisToken.ToText(), null));
case ')':
Next();
SyntaxKind closeParenthesisToken = SyntaxKind.SlashToken;
return(new SyntaxToken(closeParenthesisToken, _position, closeParenthesisToken.ToText(), null));
default:
Next();
return(new SyntaxToken(SyntaxKind.BadToken, _position, _text.Substring(_position - 1, 1), null));
}
}
